The present invention relates to a method of producing a plastics material mesh structure, comprising providing a starting material which has a pattern of holes or depressions, and stretching the starting material in at least one stretching direction to stretch out and molecularly orientate strand-forming zones of the starting material to form molecularly-oriented strands. Such a method is described in for instance GB No. 2 035 191B, GB No. 2 073 090B, GB No. 2 096 531A, GB No. 2 108 896A and GB No. 2 124 965A. The invention is applicable to such patent specifications. The definitions given in the GB specifications recited above are applicable as appropriate to the present description.
In GB No. 2 073 090B, it was found that the transmission of stress through the starting material during the initial stretching stage could be irregular, giving rise to irregular yielding of the structure; the result of such irregular yielding can be a structure in which the bars are not perfectly aligned transversely. In GB No. 2 035 191B, when carrying out the second stretch in the transverse direction on a stenter, the transverse strands may not all be stretched equally or at equal rates, causing lack of alignment of the machine direction strands or imperfect junction zones. More generally, it is desirable to increase the speed of stretching, to increase the stretch ratio applied, and to obtain better control of the stretching operation and more particularly of the position of the zone at which the structure will break if excess loads are applied in use.